Japanese Patent Publication No. 3051401 discloses the so-called three-dimensional battery using active materials formed into powders or particles. International Publication No. WO 00/59062 discloses a stacked three-dimensional battery. Further, three-dimensional batteries having a fixed layer formed by filling a particulate active material are disclosed in Japanese Patent Laid-Open Publications Nos. 2002-141101 and 2002-141104.
Since a conventional secondary battery employs active materials having the same charge and discharge characteristics, it has been generally conducted to make one battery which is chargeable and dischargeable at a large current but has a low capacity (power-ensuring battery) and another battery which is chargeable and dischargeable not at a large current but at a small current and has a high capacity (energy-ensuring battery) separately. Since the charging and discharging at a large current is incompatible with a high capacity, there exists no battery which is chargeable and dischargeable at a large current, and has a high capacity.
The following two methods can be conceived when it is required for battery system to be chargeable and dischargeable at a large current, and to have a high capacity.
(1) Connecting plural power-ensuring batteries, which are chargeable and dischargeable at a large current but has a low capacity, until a required capacity is ensured. The power of this battery assembly is too large and hence is uneconomical.
(2) Connecting plural energy-ensuring batteries, which are chargeable and dischargeable at a small current and has a high capacity, until a required power is ensured. The energy of this battery assembly is too large and hence is uneconomical.
An electrical appliance having no any rotating part, such as an electric heater, substantially requires a constant value of current throughout a starting operation and a steady operation, whereas an electrical appliance having a rotating part, such as a motor, requires instantaneously in the starting operation a value of current of about three times as high as the steady operation. When the electrical appliance having a rotating part, such as a motor, is driven by a battery, selection of a battery according to the specifications of the appliance for a steady operation will shorten the life of the battery because the battery cannot withstand instantaneous discharge of a large current in the starting operation due to the aforementioned characteristics.
An electric car, electric motorcycle or the like, in particular, requires a large current instantaneously for acceleration. Such an electric vehicle also requires a large amount of energy in order to prolong its traveling distance. For this reason, the performance of the electric car or the electric motorcycle is dependent on the performance of a battery used.
A cell starter or the like requires a large current instantaneously, which means that a large current is necessary for an instant (within a few seconds), as can be read literally. Such a cell starter, therefore does not require a large current for several ten minutes. A lead accumulator has such a characteristics. It is capable of instantaneously outputting high power, but can effectively utilize only about 10% of its whole storage energy.
The present invention, which has been devised in view of the aforementioned points, intends to attain an object to provide a hybrid battery which is capable of instantaneously outputting high power in a starting operation or the like while having an increased energy capacity by combining active materials having different charge and discharge characteristics, i.e. an power-ensuring active material and an energy-ensuring active material, into a single battery.